Yz426 shooting coolant

flattopwill

The coolant system on my '02 YZ426 is over pressurizing and shooting coolant out of the overflow. We have replaced the head gasket twice; resurfacing the head and cylinder each time.

It isn't overheating per my Trail Tech thermostat and the Pro Circuit heat strips on my radiator and head. It overheats as it runs out of coolant but not before. We put a higher pressure radiator cap on and it slowed the spit but didn't fix it.

The only suspect I can think of is if the radiators are clogged. Is there a way I can test their flow? Any other ideas?

grayracer513

The only really effective way to check the flow is by removing one tank from the core and pumping water through from the other, so you can see what comes from each tube. If you are suspicious of the radiators, I recommend sending them off to Mylers in Utah. Fast turn around (within a week) and great work.

Then again, it's pretty normal for them to overheat in a woods environment because of the lack of air flow over the radiators. If that's your problem, and the bike is otherwise mechanically sound, a small pair of fans driven by a battery will solve it.

jojo1224

If you remove the rad cap and start the bike are you getting bubbles in the coolant? It will be obvious when you see it, I had my 426 do the same after blowing a head gasket. It would instantly start blowing coolant from the overflow and the coolant hoses would be rock hard.

flattopwill

If you remove the rad cap and start the bike are you getting bubbles in the coolant? It will be obvious when you see it, I had my 426 do the same after blowing a head gasket. It would instantly start blowing coolant from the overflow and the coolant hoses would be rock hard.

flattopwill

flattopwill

I think this thing has a cracked head. I just got it back from the shop for having some transmission work done and now it's got water in the oil. It's not pushing coolant out of the overflow anymore but now it's pushing it into the oil. I replaced a gasket and O ring near the water pump but I don't think that fixed it. Will know more tomorrow.